1. Field of the Invention
The present invention relates to a method for viewing on a display unit of a client computer image data representing document data to be rendered by a print engine on a print medium according to print specifications, the client computer being arranged for exchanging data with a print server through a network, the print server being arranged for sending print instructions to the print engine, the client computer comprising a version y of a conversion function for converting document data into raster image data describing a dot arrangement to be rendered by the print engine and a version z of a client viewer application for viewing the image data according to the print specifications, the print server comprising a version x of the conversion function and a version x of the client viewer application.
The present invention also concerns an apparatus comprising a print engine, a client computer with display means for viewing image data representing document data to be rendered by the print engine on a print medium according to print specifications, a print server for sending print instructions to the print engine and arranged for exchanging data with the client computer through a network, the client computer having stored on a memory a version y of a conversion function for converting document data into raster image data describing a dot arrangement to be rendered by the print engine and a version z of a client viewer application for viewing the image data according to the print specifications, the print server having stored on a memory a version x of the conversion function and a version x of the client viewer application.
The present invention also concerns a computer program product residing on a computer readable medium comprising instructions for causing at least one process unit to carry out the method of the present invention.
2. Description of Background Art
Most networks include a number of print servers for sending print instructions to print engines and a number of client computers sharing the resources of the print servers so that many users of the network may use the print engines. Documents to be printed are sent from a client computer using a job submitter that transmits a print job from the client computer to the print server. The print jobs are executed by the print engine according to print instructions sent by the print server.
Before actually printing a document on a selected print engine, a user may need to preview the document as it will be printed by the print engine to verify that the print specifications are correct and that graphics and outline fonts will be rendered properly. The client computer is provided with a display unit, such as a monitor screen, whereon image data representing document data to be rendered by a print engine on a print medium according to print specifications can be displayed. To ensure a proper preview, a conversion function is installed on the client computer for converting document data into raster image data describing a dot arrangement as to be rendered by the print engine. The conversion function includes an interpreter function and a rasterizer function. A dedicated application software installed on the client computer, called a client viewer application, is used for viewing the image data according to the print specifications. For example, print specifications such as medium size and positioning of the image data on the medium can be checked during the preview step. Other print specifications may be also visualized, such as the orientation of the image data with respect to the print medium, the dimensions of the print margins, the position of a staple, the presence of a watermark, etc.
The print server is provided with a controller having installed thereon a conversion function. The conversion function includes an interpretation function and a rasterization function. The interpretation function of the controller examines the data sent from the client computer and identifies the command embedded in the data, such as printer control, page format, font management, text layout and graphics. The print server conversion function is used to convert the received commands into an array of dots to be rendered by the print engine. The print server is provided with a raster image processor (RIP) for executing the conversion tasks. The print server can also be provided with a version of a client viewer application in order to update the client viewer application on the client computer when this is required. This may be needed when the print engine has been upgraded with new technical features enabling the use of new print settings.
To ensure consistency between the preview displayed on the client's display unit and the image data to be printed by the print engine (i.e. a dot arrangement to be rendered by the print engine), a known method includes systematic updating of the software installed on the client computer with every update of the print server's software. According to the known method, the version of the client viewer application and the version of the conversion function on the client computer are updated each time the conversion function of a print server is updated. When a user of a client computer wishes to obtain a preview of a document to be printed on a print engine, it connects to the adequate print server in order to compare the versions of the software installed on the respective machines. The print server includes, for example, a version x of the conversion function and a version x of the client viewer application. If the versions of the conversion function and of the client viewer application on the client computer are different from the version x, a version x of the conversion function and a version x of the client viewer application are transferred to the client computer. However, this method has a number of drawbacks, such as complexity. This is particularly the case for large network systems, where many users have the ability to connect to a large number of print servers. Usually, not all print servers arranged for sending print instructions to the same type of print engine are updated at the same moment. Therefore, it happens that various print servers use different versions of the conversion function. With the known method of viewing wherein a systematic update of the client computer software is performed, the software on the client computers can have a very large footprint, because of the many versions installed thereon, which generates high costs. Moreover, the systematic upgrade might overload a print server when many users are connected concurrently to the print server.